Trailer Copyright

I've seen plenty of peers taking trailers of video games or films they have not worked on, removing the sound and applying there own music or sound design. A great way to show potential customers what they can do. The majority have clearly stated at the beginning of the video that the copyright of the work belongs to the relevant publisher/developer etc (obviously the audio copyright being an exception).

Question 1. Is it copyright infringement to do this, even if it is clearly stated at the beginning of the video that the copyright is not owned by the sound engineer/composer other than the audio elements of the trailer?

Question 2. If yes, Is it seen by potential clients, game developers, as being amateurish baring in mind that the sound engineer has fragrantly ignored copyright law?

I ask this because I would like to do it but certainly not if it is illegal, even if the risks of being sued are small because it would rub of bad on my reputation.

Bare in mind i'm UK based as there may be differences in the laws governing different countries.

Well, if you don't have a license or permission to use it, it's clearly infringement.

1) I would say, yes

2) Good question. I'm not sure how your potential clients would react, but I would assume there would be a little apprehension. The other thing you might want to consider is any backlash from the person/people that made the original audio.

I doubt you'd get sued for something like that, but there could be other repercussions.

Question, why not just make a video game trailer for a game you actually worked on?